The present invention concerns a seatback for a vehicle seat, having an integrated protective device against accident-related injuries in the event of a rear-end impact, in particular against cervical vertebra syndrome or acceleration trauma, having a lower back part joined to a seat part and having a upper back part that is pivotable relative to the lower back part out of a normal use position, about an axis extending in the seatback transversely to the longitudinal vehicle axis, through an angular range in a pivoting direction pointing in the direction of travel, as a result of a torque acting in the pivoting direction.
Many present-day developments in automotive engineering are aimed toward using available materials and design methods to make the seatbacks of vehicle seats lightweight but highly rigid, in order (despite the light weight) to withstand the large stresses that occur in an accident event and to sufficiently support the body of the vehicle occupant. The result of this, however, is that for example even in a so-called xe2x80x9cfender-benderxe2x80x9d accident or low-speed crash at low velocities in the range from 10 to 30 km/h, in which the body experiences an acceleration of approx. 8 to 20 G, damage to the body""s neck musculature and cervical vertebrae can occur, since the impact force acts in almost undamped fashion on the person. An undesirable effect, called the xe2x80x9cwhip effect,xe2x80x9d occurs on the head and neck, resulting in hyperextension and overstressing of the cervical vertebrae and support muscles of the head. This effect, and the spinal column injuries possible in particular in the neck region, are also referred to using the English term xe2x80x9cwhiplash.xe2x80x9d
Passive and active apparatuses are known for protection against these injuries; the latter, in the event of an accident, are intended to actively decrease the distance between the person""s head and the headrest of the seatback. One such known (active) apparatus of the kind cited above is described in DE 197 43 339 A1. In this context, the body of the vehicle occupant (seat user)xe2x80x94which in the event of an impact relative to the direction of travel is bent backward or accelerated, as a result of its inertia, into the seatback of the vehicle seatxe2x80x94encounters an impact panel that is mounted below the pivot axis of the upper back part and is joined pivotably to the upper back part, in particular to a headrest on the back part. The relative motion of the impact panel toward the rear causes the headrest to pivot forward. The motion of the headrest is intended to mitigate the whiplash effect.
It is disadvantageous in this context that the relative motion of the headrest does not occur until the occupant is thrown into the seatback. As a result, the upper back part can be accelerated only by a value that is equal, at most, to the acceleration value experienced by the vehicle seat as a result of the impact. Since the motion characteristics of the seat user cannot be accurately predicted in every case, however, in some circumstances the active counter-motion of the seatback or headrest may in fact cause incorrect, undesired, possibly dangerous effects. For example, the impact of the occupant""s head can in fact be further amplified, and occupant xe2x80x9crampingxe2x80x9d (vertical movement in the seat) also cannot be prevented. This is because in a rear-end impact, the occupant is accelerated into the seatback (which is usually tilted backward out of the vertical) in such a way that he or she tends to rise up along the seatback as if it were a ramp. This generally results in failure of the seatback, which buckles due to overload and is no longer capable of supporting the occupant. In particular, the seat user""s head can end up at a height which is above the headrest, where it can no longer be supported. A considerable residual accident risk thus exists with the known seatback.
Mechanisms that are triggered by displacement of the vehicle occupant""s body into the seatback opposite to the direction of travel do not exhibit the desired protective effect. The differing heights and therefore weights of vehicle users prove to be a particular disadvantage. Because of this, it is impossible to ensure reliably that the triggering device of a protective device is correct and effective. A further uncertainty factor is the delayed reaction of the previously disclosed mechanisms of this type. The configuration of the upholstery of the seatback also plays an important part; it should be as thin as possible in the region of the triggering device. This would in turn, however, result in an undesirable degradation of upholstery comfort.
It has therefore been proposed in German Patent Application 199 38 904.7 that reliable triggering of the protective device be performed, irrespective of the vehicle occupant""s build, at a minimum acceleration which can be measured, for example, at the vehicle seat. In the case of a small car, the measured acceleration value is reached at a considerably lower impact speed than is the case for a sedan with a large absorbing crumple zone, or for a truck. The proposed protective device has on the one hand a device that, irrespective of the occupancy of the vehicle seat, generates the torque acting in the pivoting direction on the upper back part; on the other hand it comprises means for detecting a rear-end impact that are in effective connection with the torque-generating device in such a way that the device is activated in the event of the rear-end impact and the pivoting motion is initiated. Also provided in this context are immobilization means for retention of the upper back part in the normal use position, and immobilization means for retention of the upper back part against a backward motion out of the safety position into the normal use position.
It is the object of the present invention to create, using means of little design complexity, a seatback of the aforesaid kind whose protective device guarantees improved protection of the respective seat user against injury, in particular by way of an improved interception capability and damping when the head and upper body of the person present on the seat strike the headrest and seatback. The intention is to implement, in particular in the normal use position and additionally in the safety position, an effective immobilization system that nevertheless does not impede the triggering operation.
The object of the invention is achieved by a seatback of the kind cited initially in which the protective device comprises at least the following parts:
a device that, irrespective of any occupancy of the vehicle seat, generates the torque acting in the pivoting direction on the upper back part;
means for detecting a rear-end impact that are in effective connection with the torque-generating device in such a way that the device is activated in the event of the rear-end impact and the pivoting motion is initiated; and
immobilization means for retention of the upper back part in the normal use position, the immobilization means being constituted by a lever system, and the means for detecting a rear-end impact being in effective connection with the immobilization means for retention of the upper back part in the normal use position in such a way that in the event of the impact, the retention of the upper back part in the normal use position is nullified.
According to the present invention, in particular because of the unlocking of the lever system, pivoting of the upper back part can preferably proceed so quickly that the upper back part is in the safety position before the onset of any head motion of the seat user resulting from the rear-end impact. In the safety position, the upper back part rests directly against the seat user""s body so that the user, despite the acceleration acting on him or her due to the impact, advantageously can no longer freely move backward against the vehicle""s direction of travel and incur accidental injuries.
In the context of the seatback according to the present invention, it is particularly advantageous in terms of the efficiency of the protective device if a headrest is attached in or on the upper back part. It is useful in this context to mount the headrest, which as a rule is guided on holding rods for adjustment of the vertical position, in the backrest at the height of the shoulder region tiltably about an axis extending transversely to the vehicle axis. For this purpose, for example, an upper crossmember of the seatback can be attached in upper portions of the side members of the seatback by means of a pivot bearing. The upper back part can also, however, be configured in such a way that it assumes the function of a headrest. In any event, the person using the vehicle seat can as a result move uniformly into the seatback with decelerating energy absorption by the vehicle seat, with particular protection of the neck and head region. The result is that when the normal use position of the seatback exists, the headrest is in a so-called comfort position in which its spacing from a seat user""s head can be approximately 40 to 110 mm. As a result of the pivoting motion of the upper back part, the headrest is then transferred into a so-called interception position, in which its spacing from a seat user""s head is zero or almost zero. The normal use position and safety position of the upper back part thus correspond, when a headrest is present, to the latter""s comfort position and interception position.
It is advantageous to provide a force storage device or energy storage device as the torque-generating device for the pivoting motion of the crossmember carrying the headrest. A preloaded torsion spring, in particular, has proven advantageous in this context, since it possesses a very low intrinsic acceleration and therefore requires less installation space for the same effect as compared to tension or compression springs.
The lever system of the immobilization means for retention of the upper back part in the normal use position can preferably comprise at least two coacting levers. A first lever (hereinafter called the pawl) can brace the pivotable crossmember, preloaded by the torsion spring, with respect to a stationary counterbearing; while a second lever (hereinafter called the immobilization lever) acts as immobilizer for the pawl. In the event of a rear-end impact, the immobilization lever is pivoted in such a way that it releases the immobilization of the pawl. Triggering of the immobilization lever can be effected with a very low actuation force, thereby making possible a very fast lever movement and thus rapid unlatching of the pawl.
Actuation of the immobilization lever can preferably be accomplished with an electromagnet which obtains its pulse from a sensor, such as an acceleration sensor, that is used as a means for detecting the rear-end impact.
After release of the pawl, the latter pivots out of its bracing position; and the crossmember of the seatback, with the headrest, can move in the direction of the back of the vehicle occupant""s head.
After a triggering of the protective device, the latter can be brought back into its initial position by once again activating the device that generates the torque acting on the upper back part (e.g. by tensioning the torsion spring); for safety reasons, this operation is to be performed only in a repair shop, in which seat functionality after a crash can concurrently also be checked.
It is particularly advantageous, in terms of reliably preventing a spring-back or bounce-back effect when the protective device takes effect, if the immobilization means for retention of the upper back part against a backward motion from the safety position into the normal use position (which means are also referred hereinafter to as the xe2x80x9crecoil lockxe2x80x9d) are embodied so that they make possible immobilization not only in the normal use position and in the safety position, but also in multiple positions located therebetween. This can be implemented, for example, by means of self-locking rolling-element or wedge-type locks that operate positively or nonpositively (preferably by jamming), or by means of a ratchet device. A suitable design of the recoil lock advantageously makes it possible to limit any recoil play of the upper back part (motion in the direction of the safety position) to a maximum angular magnitude of 1 degree.
Further advantageous embodiment features of the invention are contained in the dependent claims and in the description below.